The present invention relates to phased array antenna systems, such as radar, and more particularly relates to a beam former that generates encoded control signals that drive the antenna elements of a phased array to receive multiple beams while allowing a filter to detect coding parameters contained in the control signals to separate the multiple beams from a combined signal received from the antenna.
Phased array antenna systems, such as those used for radar systems, take advantage of the phase differential that occurs according to the direction of coherent propagating energy. For example, in a simple array of two closely spaced antenna elements lying in a plane and both facing forward, an incoming signal coming straight from the forward direction would be received at the same time at both elements, resulting in signals at each element having the same phase, which are referred to as xe2x80x9cin-phase.xe2x80x9d But if the energy approaches the elements at an angle, the two elements receive the energy at different times, resulting in a phase differential or xe2x80x9cshiftxe2x80x9d between the two signals. This is similar to ocean waves arriving at a beach. If the wave comes straight in to shore, the wave washes upon the beach at the same time along the beach. If the wave is coming in at an angle relative to the beach, however, it arrives first in one spot and then progressively arrives down the beach at later times.
A similar phenomenon is at work in phased array antenna systems. Since the propagating electromagnetic energy reaches the nearest antenna element first, the direction of the incoming energy can be determined by detecting the phase differential. Similarly, a directional xe2x80x9cbeamxe2x80x9d may be formed by collecting the signals from the antenna elements with coordinated phase delays, which causes the received energy to add up constructively in a desired beam direction while partially or completely canceling out in all other directions. It is common to steer a coherent beam created in this manner by controlling programmable phase and gain control devices at each antenna element in a coordinated manner. For example, a single beam formed by a phased array may be controlled to periodically sweep across the antenna""s angular coverage, to track a detected target, to sweep or track while avoiding a known signal, or to achieve other objectives. This conventional single-beam steering system uses a single controllable phase and gain control device for each antenna element, a single beam forming combiner, and a beam steering computer to create and control the beam.
It is also conventional to use a phased array antenna system to simultaneously receive multiple beams having different pointing directions. For example, rather than steering one beam to sweep across the antenna""s angular coverage, as described above, the phased array may be controlled to divide the antenna""s angular coverage into multiple beams to monitor the entire operational volume simultaneously. This may be thought of as causing the antenna to xe2x80x9clookxe2x80x9d in many different directions at the same time. This is accomplished conventionally by dividing the signal received at each antenna element into separate channels using separate phase and gain control devices at each antenna element for each desired beam. In addition, a separate beam forming combiner is typically required to assemble each beam from the signals received for the corresponding beam from each antenna element. In other words, the multiple beams are conventionally formed by providing separate sets of antenna hardware for each beam, which generally multiplies the required number of antenna hardware elements, including phase and gain control devices and beam forming combiners, by the number of desired beams. This may be considered a xe2x80x9cbrute forcexe2x80x9d design technique due to the heavy dependence on antenna hardware to generate the desired beams.
In a typical target acquisition radar, for example, the phased array antenna may include 1,000 antenna elements that are used to form 100 independently controlled beams. In this case, each of the 1,000 antenna elements requires 100 different simultaneous phase and gain settings to form the 100 different beams. This is conventionally accomplished by providing each of the 1,000 antenna elements with 100 different phase and gain devices, one corresponding to each beam. The signals for each beam received from the various antenna elements are then combined in a separate beam forming combiner to create 100 different beams, each having a component received from each antenna element. This conventional approach requires 100,000 phase and gain devices and 100 beam forming combiners, which typically results in a system that is exorbitantly expensive, complex to construct, large in size, and heavy. Any one or more of these penalties may be critical for a particular application.
To save against these penalties, the beams may be set in advance by fixed phase and gain control devices, which cannot be changed without changing the antenna hardware. This option, of course, limits the flexibility of the system. Alternatively, the antenna may include programmable control hardware that can be reprogrammed to create different beam sets, which may involve defining the number of beams, their pointing directions, and the shapes of their antenna patterns. However, this approach may be prohibitively expensive because it requires separate programmable phase and gain control devices for each antenna element, for each desired beam. For the antenna in the previous example, this would require 100,000 programmable phase and gain control devices. The number of beams or antenna elements may be reduced, but performance is sacrificed with these alternatives.
In addition, a conventional single-beam radar system typically includes a single phase and gain device for each antenna element, a single beam forming combiner, and a Doppler filter. In many such cases, the beam forming network produces a sum and two difference beams for mono-pulse operation. Upgrading such a system to receive multiple beams in the conventional manner, as described above, would require multiplying the number of phase and gain control devices at each antenna element by the number of desired beams, and adding a separate beam forming combiner and Doppler filter for each desired beam. Again, size, weight or cost constraints may ultimately limit the number of beams that can be accommodated in the upgrade. The design penalties would be minimized, of course, if multiple beams could be produced while requiring only a single phase and gain control device for each antenna element and a single combiner and Doppler filter for all of the beams. But such systems are not presently available.
Accordingly, a need exists for improved methods and systems for receiving multiple beams with a phased array antenna system. A further need exists for methods and systems for upgrading existing single-beam phased array antenna systems to receive multiple beams. In particular, a need exists for phased array antenna systems that can receive multiple beams without relying on multiple phase and gain control devices for each antenna element, and without dedicating separate beam formers for each beam.
The present invention meet the needs described above in a phased array antenna system that uses an intelligent beam former to drives the antenna array to receive multiple beams using a single programmable phase and gain control device for each antenna element and a single combiner and beam former for all of the beams. The intelligent beam former encodes each beam, combines the encoded beams into a combined signal, and then separates the multiple beams from the combined signal. For example, the beams may be code division multiplexed using orthogonal codes, and the beams may be decoded to separate the beams using an orthogonal code filter, such as a conventional CDMA filter. Alternatively, the beams may be frequency coded and decoded to separate the beams with a frequency filter. In a particular frequency coding example, the beams may be frequency coded by repeatedly incrementing phase shifts applied to identify beam components, and the beams may be decoded to separate the beams using a conventional Doppler filter.
Advantageously, the present invention may be used to create a multi-beam phased array antenna system using a single programmable phase and gain control device for each antenna element, a single beam forming combiner for the array, and a single beam decoder or filter for the array. That is, the invention allows a beam encoder implemented through software running on a beam forming computer, and a cooperating beam decoder, such as a conventional CDMA or Doppler filter, to effectively replace the multiplicity of antenna hardware found in conventional multi-beam phased array antenna systems. In addition, a conventional single-beam phased array antenna system may already include at least one programmable phase and gain control device for each antenna element, at least one beam forming combiner, at least one beam forming computer, and at least one Doppler filter. For this reason, the present invention may be used to upgrade many conventional single-beam phased array antenna systems to multi-beam systems without the need for extensive additional hardware.
Further, appropriate beam coding sequences for a known CDMA or Doppler filter can be determined in advance and stored in a look-up table. This allows the multi-beam controller to operate at high data rates with low computational overhead. The beam forming computer may also change the beam pattern on demand to implement target tracking and other design objectives. The beam forming computer may also change the code sets on demand, or switch between coding methodologies on demand to avoid interference on certain channels or achieve other objectives. Since the present invention implements all of these capabilities through software applied to standard antenna hardware, a very wide range of phased array antenna systems can be manufactured or upgraded to include these capabilities without substantially increasing the cost, complexity, size, or weight of the system.
Generally described, the methodology of the invention may be implemented on a beam forming computer, which may be local or remote, or it may be expressed in computer-executable instructions stored on a computer storage medium. The beam forming computer implements a method for operating a phased array antenna system to receive propagating energy at multiple antenna elements, and to form the received energy into multiple beams. In particular, the beam forming computer encodes the received beams and combines the encoded beams into a combined signal. This allows a cooperating filter to decode the combined signal to separate the beams. Typically, the system also includes a device that displays and records a representation of each beam separately.
In addition, a beam selector may obtain antenna parameters defining locations for the antenna elements and beam specifications defining pointing directions for a desired set of multiple beams. The beam selector then uses the antenna parameters and beam specifications to define control signals for forming the received energy into the desired set of beams. The beam forming computer then embeds coding parameters into the control signals, and applies the encoded control signals to phase and gain control devices associated with each antenna element. This methodology may be repeated for different desired beam sets, which allows the system to change beams on demand to track a detected target, to monitor a space while avoiding a known signal, or to achieve other objectives.
Further, a code selector may obtain coding parameters for different desired coding strategies, such as different frequency code sets and different orthogonal code sets. The beam forming computer embeds these coding parameters into the control signals, and applies the encoded control signals to phase and gain control devices associated with each antenna element. This methodology may be repeated for different desired coding parameter sets, which allows the system to change coding strategies on demand to avoid channels with interference or to achieve other objectives. In addition, the code selector, the beam selector, and the beam forming computer may be implemented on separate computing devices, or they may be implemented on a single computing machine.
The control signal for each antenna element may be applied to a single phase and gain control device dedicated to the corresponding antenna element. In this case, the control signal for each antenna element includes the vector sum of beam components corresponding to each beam. Alternatively, each antenna element may include a plurality of phase and gain control devices with one phase and gain control device dedicated to each beam. In this case, the control signal for each antenna element is applied to the plurality of phase and gain control devices associated with the corresponding antenna element, with each phase and gain control device receiving the control signal component for a corresponding beam. In either case, the encoded beams are combined in a beam forming combiner, and the multiple beams are separated from the combined signal using a filter that is designed to detect the coding parameters embedded into the control signals by the beam forming computer.
More specifically, the beam forming computer typically forms the received energy into multiple beams by defining a control signal for each antenna element, in which each control signal includes a beam component corresponding to each beam. The beam forming computer then encodes the beams by embedding a coding parameter into each beam component identifying the corresponding beam. Using the same coding parameter for a corresponding beam at each antenna element allows the beam decoder to identify the beam components by detecting the coding parameters as they are reflected in the combined signal, and to extract and combine the components having similar coding parameters to assemble the various beams.
On the encoding side, the beam forming computer preferably computes an in-phase component for the control signal for each antenna element as a sum of in-phase beam components for the corresponding antenna elements. That is, the control signal for each antenna element typically includes one in-phase component for each beam. Similarly, the beam forming computer also preferably computes a quadrature component for the control signal for each antenna element as a sum of quadrature beam components for the corresponding antenna elements. Again, the control signal for each antenna element typically includes one quadrature component for each beam. The beam forming computer then computes a total gain and a total phase shift for each antenna element from the corresponding in-phase and quadrature components. For example, the total gain and total phase for a particular antenna element is typically computed as the vector sum of the beam component vectors for that antenna element, in which a coding parameter has been embedded into the in-phase and quadrature beam components for each antenna element.
A beam decoder later detects these coding parameters to identify the beam components, which are assembled into the separate beams for further processing, display, or recording. For example, using the same coding parameter for a corresponding beam in the control signal for each antenna element allows the filter to assemble the beams directly by detecting the coding parameters and combining the components having similar parameters into corresponding beams. Further, using channel indicatory as the coding parameters allows the decoder to directly assign the assembled beams to corresponding channels. Although this type of direct beam component identification and channel assignment scheme is computationally efficient and straightforward to implement, other more complicated indirect beam component identification and channel assignment schemes may be employed.
For example, the coding parameters used to encode a particular beam need not be identical for each antenna element so long as there is some appropriate correlation system for identifying which components go with which beam on the decoding side. In particular, using the same beam parameter to identify the components for a particular beam at each antenna element is a straightforward way to accomplish this result, which obviates the need for a correlation step on the decoder end. Nevertheless, other decoding schemes, such as those using a correlation table, correlation formula or other appropriate mechanism may be used to associate detected components into the desired beams. Further, the decoder may be synchronized with the precise coding parameters that are embedded into the control signals, or there may be a correlation step used to associate the detected coding parameters with those used by the decoder to assemble the beams and assign the beams to channels. In addition, the coding parameters may themselves indicate channels for further processing, displaying or recording the beams, or there may be an intermediate step to assign the assembled beams to channels.
Further, many other coding, decoding, channel assignment, and correlation schemes will become apparent using the basic beam encoding approach of the present invention. But in every such system, the decoder directly or indirectly detects the coding parameters, which the encoder embedded into control signals to permit beam component identification, and uses the detected coding parameters directly or indirectly to identify which components form which beams. Once this has been accomplished, many different schemes may be employed to assemble the beams and assigned the assembled beams to channels for further processing, display, or recording.
In one embodiment, the beams are encoded with frequency codes and decoded with a conventional Doppler filter, which serves as the beam decoder. That is, the beams are encoded by embedding frequency shifting parameters into the in-phase and quadrature beam components, and the beams are later decoded with the Doppler frequency filter and assembled in the manner described above. In another embodiment, the beams are encoded with orthogonal codes and decoded with a conventional CDMA filter, which serves as the beam decoder. Again, the beams are encoded by embedding orthogonal codes into the in-phase and quadrature beam components, and the beams are later decoded with the CDMA orthogonal code filter and assembled in the manner described above.
The invention may be used to implement a multi-beam phased array antenna system that includes a plurality of antenna elements, one or more phase and gain control devices for each antenna element, and a typically a single beam forming combiner creating a combined signal from the signals received from the antenna elements. As described above, a beam forming computer is configured to generate control signals to drive the phase and gain control devices to create multiple beams, in which each beam is identified by a coding parameter embedded into the control signals. In addition, a filter is configured to receive the combined signal, detect the coding parameters, and separate the beams using the coding parameters.
The antenna system may also include a beam selector configured to identify desired beam sets. In this case, the beam forming computer is configured to generate control signal to drive the phase and gain control devices to create multiple beams for each desired beam set defined by the beam selector. Further, the antenna system may include a code selector configured to identify desired coding parameter sets. In this case, the beam forming computer is configured to generate control signals to drive the phase and gain control devices to create multiple beams for each desired coding parameter set defined by the code selector. As noted above, the coding parameter sets may include orthogonal code and frequency code sets.
In view of the foregoing, it will be appreciated that the present invention avoids the drawbacks of prior methods for creating multi-beam phased array antenna systems. The specific techniques and structures for creating multiple-beams with minimal antenna hardware, and thereby accomplishing the advantages described above, will become apparent from the following detailed description of the embodiments and the appended drawings and claims.